OBJECTIVE: To identify the nucleus retroambiguus (NRA), and find projections from this nucleus to the lumbosacral cord. RESULTS In the first experiment, to determine the location of the NRA, the tracer wheat-germ agglutinin horseradish peroxidase (WGA-HRP) was injected into the lumbosacral enlargement in two ovariectomized female monkeys. The labeled cells in the NRA were found at the levels 2 to 4 mm caudal to the obex. In the second experiment, to identify projection from the NRA to the lumbosacral cord WGA-HRP was injected into the NRA in three ovariectomized monkeys. Further to identify the motoneurons innervated by the NRA, cholera toxin subunit-b was injected into the m. semimembranosus, m. iliopsoas, m. obliquus externus, m. sphincter ani externus, and m. longissimus medialis of the same 3 monkeys. It was found that anterogradely labeled fibers from the NRA project predominantly to the contralateral spinal cord, where they target motoneurons innervating the abdominal wall, iliopsoas, and pelvic floor muscles. FUTURE DIRECTIONS We will examine the effects of estrogen on this pathway. KEY WORDS nucleus retroambiguus, lumbosacral cord, anterograde track trace.